Technical Field
The present disclosure relates to liquid lifting devices and liquid lifting methods configured to pump up liquid stored at a low position to a higher position using an air pump.
Background Art
Liquid lifting devices using an air pump (or vacuum pump) are a device in which one end of a liquid lifting pipe is inserted into a liquid source placed at a low position, the other end of the liquid lifting pipe is connected to a tank having an airtight structure and provided at a higher position, and the interior of the tank is depressurized by the air pump so as to pump up liquid in the liquid source to the tank through the liquid lifting pipe. However, with this type of liquid lifting device, liquid cannot be lifted to a height equal to or higher than a potential liquid lifting height corresponding to negative pressure generated by the air pump.
As such, Patent Document 1 proposes a liquid lifting device capable of lifting liquid to a height equal to or higher than a potential liquid lifting height by a vacuum pump. FIG. 10 shows an example of the proposed device, which includes a liquid source 100 provided at a low position, a liquid lifting pipe 101 whose one end is inserted into the liquid source 100, a tank 102 provided at a higher position and to which the other end of the liquid lifting pipe 101 is connected, and a vacuum pump 103 provided in the tank 102. The other end of the liquid lifting pipe 101 is disposed at a height equal to or higher than a potential liquid lifting height by the vacuum pump 103 relative to a liquid surface level of the liquid source 100. An air supply pipe 104 is connected to the liquid lifting pipe 101 at a position halfway in the liquid lifting pipe 101 and lower than the potential liquid lifting height by the vacuum pump 103. An air supply valve 105 is attached to the air supply pipe 104.
In the case where the vacuum pump 103 is driven in a state where the air supply valve 105 is closed, air in the tank 102 connected to the vacuum pump 103 and air in the liquid lifting pipe 101 are discharged so that the interiors thereof are depressurized. When the interior of the liquid lifting pipe 101 is under a predetermined negative pressure, a liquid surface in the liquid lifting pipe 101 rises up to a position higher than a branching section to which the air supply pipe 104 is connected. However, the liquid surface cannot reach the height of the tank 102. Here, in the case where the air supply valve 105 is opened for a short time, air is introduced into the air supply pipe 104 and stays in the branching section as an air bubble 106 in the liquid lifting pipe 101 so that the liquid in the liquid lifting pipe 101 is divided into upper side and lower side liquids. The air bubble 106 ascends due to a difference between pressure in the liquid lifting pipe 101 and pressure of the air bubble 106 and a buoyant force that the air bubble 106 receives. As such, a liquid column positioned on the upper side of the air bubble 106 is pushed upward and consequently flows into the tank 102.
However, in the liquid lifting device configured as described above, since the air supply pipe 104 which is short in length is connected to a side portion of the liquid lifting pipe 101 and the air supply valve 105 is attached to the air supply pipe 104, liquid makes contact with the air supply valve 105. Because of this, impurities contained in the liquid adhere to the valve 105, which raises a risk that the open/close operation of the valve 105 is carried out incorrectly. In addition, in the case where the air supply valve 105 is opened for more than a predetermined time, there arises a risk that the liquid flows out through the air supply valve 105.
Another embodiment, which is different from the liquid lifting device discussed above, is also disclosed in Patent Document 1. FIG. 11 shows an example of the stated embodiment, where an air delivery pipe 104 is inserted into the liquid lifting pipe 101 and a lower end thereof is opened at a position lower than the potential liquid lifting height by the vacuum pump 103. To an upper end of the air delivery pipe 104, an openable/closable valve 105 that is intermittently opened/closed is attached. In this embodiment, because the openable/closable valve 105 is attached to the upper end of the air delivery pipe 104 projecting above the liquid lifting pipe 101, there is not a risk that liquid makes contact with the openable/closable valve 105, and a problem that the liquid flows out of the air delivery pipe 104 is not present as well.
However, in this liquid lifting device, since the air delivery pipe 104 is inserted into the liquid lifting pipe 101, a cross-sectional area of the liquid lifting pipe 101 is decreased by a cross-sectional area of the air delivery pipe 104 and a circular gap between the liquid lifting pipe 101 and the air delivery pipe 104 is a liquid flow path. An air layer introduced through the air delivery pipe 104 stays at a leading end of the air delivery pipe 104 as the air bubble 106; this air bubble 106 needs to divide the liquid filled in the circular gap between the liquid lifting pipe 101 and the air delivery pipe 104 into upper side and lower side liquids. However, in order to divide the liquid filled in the circular gap into the upper and lower side liquids, a large air bubble needs to be created. Patent Document 1 discloses that operation to open the openable/closable valve 105 for a short time is repeatedly carried out so that a plurality of air bubbles are intermittently discharged and the plurality of discharged air bubbles are gathered as they ascend, whereby a shell-shaped air bubble (slug flow) is formed so as to occupy the caliber of the liquid lifting pipe 101 (see paragraph 0022). However, it is not always the case that a plurality of air bubbles are gathered to be formed into a single bubble in the circular space, which raises a risk that the liquid filled in the circular gap cannot be divided into upper and lower side liquids and a desired liquid lifting effect cannot be achieved. Further, in the case where the invention of Patent Document 1 is applied to a small liquid lifting device including the liquid lifting pipe 101 with a relatively small diameter, there is a risk that the air bubble keeps staying at the leading end of the air delivery pipe 104 due to influence of the surface tension of liquid and cannot ascend in the circular gap of the liquid lifting pipe 101.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-240600